Pollution Characteristics And Influencing Factors Of Particulate Organic Nitrates In Typical Areas In Eastern China

Particulate organic nitrates are important components of secondary organic aerosols and have a significant contribution to atmospheric fine particulate matters.They have significant impacts on regional nitrogen budget,ozone production,and cloud formation.Previous studies have shown that biogenic volatile organic compounds(BVOCs),such as pinene and limonene,are important precursors of organic nitrates.At present,studies on particulate organic nitrates in the atmospheric environment are mainly carried out in Europe and the United States.The relevant research work is still lacking under the conditions of high NOx emission and severe particulate matters pollution in China,where the pollution characteristics,chemical composition,and influencing factors of particulate organic nitrates remain unclear.In this study,fine particulate matter samples were collected at the rural site of Dongying and urban sites of Beijing,Jinan,Nanjing,and Guangzhou in eastern China.The organic matters were extracted with methanol,and the extracts were concentrated and filtered.The content of six kinds of particulate organic nitrates,including monoterpene hydroxyl nitrate(MHN215),pinene keto nitrate(PKN229),monoterpene dicarbonyl nitrate(MDCN247),oleic acid keto nitrate(OAKN359),oleic acid hydroxyl nitrate(OAHN361),and pinene sulfate organic nitrate(PSON295),were determined using high-performance liquid chromatography-mass spectrometryThe measurement results show that the total concentration of six kinds of particulate organic nitrates ranged from 113 to 415 ng/m3,and the average contribution to organic aerosol was from 0.7%to 4.7%.Among the six species of organic nitrates,MHN215 was the dominant component with an average proportion of 37%to 51%,followed by OAKN359 and PKN229.The concentration of particulate organic nitrates in summer was higher than that in winter due to the high concentrations of BVOCs and photochemical oxidants in summer.The concentration of MHN215 during daytime at Dongying site in summer was higher than that during nighttime;however,the diurnal differences of particulate organic nitrates at other sampling sites were not obvious.Case analyses show that the concentration of particulate organic nitrates in North China was clearly influenced by human activities such as biomass burning and coal combustion,while the atmospheric relative humidity and biogenic emission were the major contributing factors in South China.Biomass burning significantly enhanced the generation of particulate organic nitrates due to the elevated ozone concentration and BVOC emissions at the Dongying site in summer.Coal combustion activities increased the concentration of particulate organic nitrates in the downwind area at the Jinan and Dongying sampling site in winter.Moreover,particulate organic nitrates had a strong correlation with SO2 concentration,suggesting that SO2 and acidic aerosols in coal combustion plumes possibly promoted the production of organic nitrates.At the Guangzhou site,when the relative humidity was high(>70%),the concentration of particulate organic nitrates increased significantly.It is speculated that liquid-phase reactions were possibly potential pathway for the production of organic nitrates.